Method and apparatus for retrieving a transmission opportunity control in reverse direction grant

ABSTRACT

Embodiments of the present invention disclose a method and an apparatus for retrieving transmission opportunity control in reverse direction grant, so that a conflict occurring between a case where an RD Initiator continues sending another frame to an RD Responder after retrieving TXOP control and a case where a terminal other than the RD Initiator sends a block acknowledgement to the RD Responder can be avoided. The method provided in the embodiments of the present invention includes: when an RD Initiator fails to correctly demodulate a frame sent by an RD Responder, retrieving, by the RD Initiator, TXOP control by using a PIFS if it is impossible for the RD Responder to enable an MU-MIMO mode, and retrieving, by the RD Initiator, the TXOP control by using a duration if it is possible for the RD Responder to enable the MU-MIMO mode, where the duration is longer than the PIFS.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/689,445, filed on Nov. 29, 2012, which is a continuation ofInternational Patent Application No. PCT/CN2012/072698, filed on Mar.21, 2012. The International Application claims priority to ChinesePatent Application No. 201110276060.2, filed on Sep. 16, 2011. Theafore-mentioned patent applications are hereby incorporated by referencein their entireties.

FIELD OF THE INVENTION

The present invention relates to the field of communicationstechnologies, and in particular, to a method and an apparatus forretrieving transmission opportunity control in reverse direction grant.

BACKGROUND OF THE INVENTION

A basic service set (BSS) is a basic element of a wireless local areanetwork (WLAN). A BSS network is formed by stations (STA) that havecertain association within a specific coverage area. One scenario of theassociation is that stations directly communicate with each other in anad hoc network, which is called an independent BSS (IBSS). Anothercommon scenario is that in a BBS network, only one central station fordedicatedly managing a BSS is called an access point (AP), whereas otherstations that are not an AP are called terminals, or called non-AP STAs.The AP and non-AP STAs are collectively called STAs. The AP and non-APSTAs do not need to be distinguished in description of the STA. In thesame BSS network, due to factors such as a distance and transmit power,one STA is incapable of detecting another STA that is far away from it.The two STAs are hidden nodes for each other.

In the 802.11e protocol, a transmission opportunity (TXOP) isintroduced. A TXOP is a bounded time interval during which a station maytransmit a frame in a specific communication category. The stationobtains a TXOP through contention. Once obtaining the TXOP, the stationmay transmit a frame in a specific communication category within theTXOP. The frame may specifically be a data frame, a control frame, or amanagement frame.

When a certain STA obtains a TXOP through contention, the STA is calleda TXOP holder. A technology that within the TXOP, when the TXOP holderdoes not transmit data itself, the TXOP holder temporarily transfersTXOP control to another STA, and the another STA that is enabled to senddata to the TXOP holder is called reverse direction grant (RDG). In theRDG, the TXOP holder is called a reverse direction initiator (RDInitiator), and the STA that temporarily obtains the TXOP controlgranted by the RD Initiator is called a reverse direction responder (RDResponder).

To fully use a spectrum resource and improving a transmission rate, aTXOP sharing mode of multi-user multiple input multiple-output (MU-MIMO)is defined for downlink data of an AP. In this TXOP sharing mode of theMU-MIMO, multiple service types may share one TXOP, so as to implementconcurrent transmission of frames of multiple service types in anMU-MIMO mode, thereby greatly saving the spectrum resource.

In traditional RDG, when an RD Responder sends a last frame to an RDInitiator, or requires an RD Initiator to send a block acknowledgementfor the frame, the RD Responder automatically returns TXOP control backto the RD Initiator.

If the RD Initiator correctly demodulates the last frame sent by the RDResponder, the RD Initiator immediately retrieves the TXOP control. Whenthe RD Responder sends a block acknowledgement request (BAR), the RDInitiator returns a block acknowledgement (BA) to the RD Responder. Whenthe RD Initiator fails to correctly demodulate a block acknowledgementframe, the RD Initiator retrieves the TXOP control by using a pointcoordination function inter-frame space (PIFS). Retrieving the TXOPcontrol by using the PIFS means that when the RD Initiator fails tocorrectly demodulate a frame, and does not know whether the frame is alast frame and whether a block acknowledgement is needed for the frame,within one PIFS, the RD Initiator intercepts a state of a channel (busyor idle). If the channel is in an idle state within the PIFS, the RDInitiator retrieves the TXOP control.

Based on the traditional RDG, when the RD Responder is an AP thatsupports the MU-MIMO, the AP may use an MU-MIMO technology to improvethe transmission rate. For example, in a specific scenario, existingstations are an AP, an STA1, and an STA2. The STA1 and the STA2 arehidden nodes for each other, the RD Initiator is the STA1, and the RDResponder is the AP. When the AP enables the MU-MIMO, concurrently sendsa frame to the STA1 and the STA2, and requires the STA2 to send anacknowledgement in time, if the STA1 fails to correctly demodulate theframe, the STA1 retrieves TXOP control by using a PIFS and thencontinues sending another frame to the AP. However, in this case, theSTA2 sends a BA to the AP according to a requirement of the AP. That is,at the same time point, the STA1 sends another frame to the AP and theSTA2 sends a BA to the AP, thereby resulting in a conflict.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a method and an apparatusfor retrieving transmission opportunity control in reverse directiongrant, so that a conflict occurring between a case where an RD Initiatorcontinues sending another frame to an RD Responder after retrieving TXOPcontrol and a case where a terminal other than the RD Initiator sends ablock acknowledgement to the RD Responder can be avoided.

In one aspect, an embodiment of the present invention provides a methodfor retrieving transmission opportunity control in reverse directiongrant, where the method includes:

when a reverse direction initiator RD Initiator fails to correctlydemodulate a frame sent by a reverse direction responder RD Responder,retrieving, by the RD Initiator, transmission opportunity TXOP controlby using a point coordination function inter-frame space PIFS if it isimpossible for the RD Responder to enable a multi-user multiple-inputmultiple-output MU-MIMO mode, and retrieving, by the RD Initiator, theTXOP control by using a duration if it is possible for the RD Responderto enable the MU-MIMO mode, where the duration is longer than the PIFS.

In another aspect, an embodiment of the present invention provides amethod for retrieving transmission opportunity control in reversedirection grant, where the method includes:

when a reverse direction initiator RD Initiator fails to correctlydemodulate very high throughput signaling A1 in a frame sent by areverse direction responder RD responder, retrieving, by the RDInitiator, transmission opportunity TXOP control by using a pointcoordination function inter-frame space PIFS if it is impossible for theRD Responder to enable a multi-user multiple-input multiple-outputMU-MIMO mode, and retrieving, by the RD Initiator, the TXOP control byusing a duration if it is possible for the RD Responder to enable theMU-MIMO mode, where the duration is longer than the PIFS;

when the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, retrieving, by the RDInitiator, the TXOP control by using the PIFS if the frame is asingle-user frame and a value of a partial association identifierPartial AID in the very high throughput signaling A1 is the same as avalue of a Partial AID of the RD Initiator;

when the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, retrieving, by the RDInitiator, the TXOP control by using a duration if the frame is amulti-user frame, where the duration is longer than the PIFS; and

when the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, retrieving, by the RDInitiator, the TXOP control by using a duration if the frame is asingle-user frame and the value of the partial association identifierPartial AID in the very high throughput signaling A1 is different fromthe value of the Partial AID of the RD Initiator, where the duration islonger than the PIFS.

In another aspect, an embodiment of the present invention provides amethod for retrieving transmission opportunity control in reversedirection grant, where the method includes:

when a reverse direction responder RD responder enables a multi-usermultiple-input multiple-output MU-MIMO mode, and the RD responderconcurrently sends a frame to a plurality of stations that include areverse direction initiator RD Initiator, requiring only the RDInitiator to send a block acknowledgement, so that the RD Initiator iscapable of retrieving transmission opportunity TXOP control.

In one aspect, an embodiment of the present invention provides a reversedirection initiator RD Initiator, including:

a first control retrieving unit, configured to, when a reverse directioninitiator RD Initiator fails to correctly demodulate a frame sent by areverse direction responder RD Responder, retrieve transmissionopportunity TXOP control by using a point coordination functioninter-frame space PIFS if it is impossible for the RD Responder toenable a multi-user multiple-input multiple-output MU-MIMO mode; and

a second control retrieving unit, configured to, when the RD Initiatorfails to correctly demodulate the frame sent by the RD Responder,retrieve the TXOP control by using a duration if it is possible for theRD Responder to enable the MU-MIMO mode, where the duration is longerthan the PIFS.

In another aspect, an embodiment of the present invention provides areverse direction initiator RD Initiator, including:

a first control retrieving unit, configured to, when a reverse directioninitiator RD Initiator fails to correctly demodulate a very highthroughput signaling A1 in a frame sent by a reverse direction responderRD responder, retrieve transmission opportunity TXOP control by using apoint coordination function inter-frame space PIFS if it is impossiblefor the RD Responder to enable a multi-user multiple-inputmultiple-output MU-MIMO mode; and

a second control retrieving unit, configured to, when the RD Initiatorfails to correctly demodulate the very high throughput signaling A1 inthe frame sent by the RD responder, retrieve the TXOP control by using aduration if it is possible for the RD Responder to enable the MU-MIMOmode, where the duration is longer than the PIFS;

a third control retrieving unit, configured to, when the RD Initiatorcorrectly demodulates the very high throughput signaling A1 in the framesent by the RD responder but fails to correctly demodulate the framecompletely, retrieve the TXOP control by using the PIFS if the frame isa single-user frame and a value of a partial association identifierPartial AID in the very high throughput signaling A1 is the same as avalue of a Partial AID of the RD Initiator;

a fourth control retrieving unit, configured to, when the RD Initiatorcorrectly demodulates the very high throughput signaling A1 in the framesent by the RD responder but fails to correctly demodulate the framecompletely, retrieve the TXOP control by using a duration if the frameis a multi-user frame, where the duration is longer than the PIFS; and

a fifth control retrieving unit, configured to, when the RD Initiatorcorrectly demodulates the very high throughput signaling A1 in the framesent by the RD responder but fails to correctly demodulate the framecompletely, retrieve the TXOP control by using a duration if the frameis a single-user frame and the value of the partial associationidentifier Partial AID in the very high throughput signaling A1 isdifferent from the value of the Partial AID of the RD Initiator, wherethe duration is longer than the PIFS.

In one aspect, an embodiment of the present invention provides a reversedirection responder RD Responder, where:

when the RD Responder is configured to, when the RD responder enables amulti-user multiple-input multiple-output MU-MIMO mode, and the RDresponder concurrently sends a frame to a plurality of stations thatinclude a reverse direction initiator RD Initiator, require only the RDInitiator to send a block acknowledgement, so that the RD Initiator iscapable of retrieving transmission opportunity TXOP control.

It can be seen from the foregoing technical solutions that, theembodiments of the present invention have the following advantages.

In an embodiment of the present invention, when an RD Initiator fails tocorrectly demodulate a frame sent by an RD Responder, the RD Initiatorretrieves TXOP control by using a duration if it is possible for the RDResponder to enable an MU-MIMO mode, where the duration is longer than aPIFS. Because the RD Initiator retrieves the TXOP control by using aduration that is longer than the PIFS, that is, within the duration thatis longer than the PIFS, a terminal other than the RD Initiator sends ablock acknowledgment to the RD Responder, and then the RD Respondercontinues sending a frame. In this case, the RD Initiator may interceptthat a channel is in a busy state, and does not retrieve the TXOPcontrol, thereby avoiding a conflict occurring between a case where theRD Initiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder. If it isimpossible for the RD Responder to enable the MU-MIMO mode, it isimpossible for the RD Responder to concurrently send a frame to the RDInitiator and the terminal other than the RD Initiator. Therefore, aconflict occurring between a case where the RD Initiator continuessending another frame to the RD Responder after retrieving the TXOPcontrol and a case where the terminal other than the RD Initiator sendsa block acknowledgement to the RD Responder does not occur.

In another embodiment of the present invention, when an RD Initiatorfails to correctly demodulate a very high throughput signaling in aframe sent by an RD responder, the RD Initiator retrieves TXOP controlby using a duration if it is possible for the RD Responder to enable anMU-MIMO mode, where the duration is longer than a PIFS. Because the RDInitiator retrieves the TXOP control by using a duration that is longerthan the PIFS, that is, within the duration that is longer than thePIFS, a terminal other than the RD Initiator sends a blockacknowledgment to the RD Responder, and then the RD Responder continuessending a frame. In this case, the RD Initiator may intercept that achannel is in a busy state, and does not retrieve the TXOP control,thereby avoiding a conflict occurring between a case where the RDInitiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder.

When the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, the RD Initiator retrievesthe TXOP control by using the PIFS if the frame is a single-user frameand a value of a Partial AID in the frame is the same as a value of aPartial AID of the RD Initiator. Because the frame sent by the RDResponder to the RD Initiator is a single-user frame, that is, the frameis sent only by the RD Responder to the RD Initiator, it is impossiblefor the RD Responder to concurrently send a frame to the RD Initiatorand the terminal other than the RD Initiator. Therefore, a conflictbetween a case where the RD Initiator continues sending another frame tothe RD Responder after retrieving the TXOP control and a case where theterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder does not occur.

When the RD Initiator satisfies one of the following conditions, the RDInitiator retrieves the TXOP control by using a duration that is longerthan the PIFS. The following conditions are: The frame is a multi-userframe; and the value of the Partial AID in the very high throughputsignaling A1 is different from the value of the Partial AID of the RDInitiator. Because the RD Initiator retrieves the TXOP control by usinga duration that is longer than the PIFS, that is, within the durationthat is longer than the PIFS, a terminal other than the RD Initiatorsends a block acknowledgment to the RD Responder, and then the RDResponder continues sending a frame. In this case, the RD Initiator mayintercept that a channel is in a busy state, and does not retrieve theTXOP control, thereby avoiding a conflict occurring between a case wherethe RD Initiator continues sending another frame to the RD Responderafter retrieving the TXOP control and a case where the terminal otherthan the RD Initiator sends a block acknowledgement to the RD Responder.

In another embodiment of the present invention, when an RD responderenables an MU-MIMO mode, and the RD responder concurrently sends a frameto a plurality of stations that include an RD Initiator, only the RDInitiator is required to send a block acknowledgement, so that the RDInitiator is capable of retrieving TXOP control. Because the RDResponder requires only the RD Initiator to send a block acknowledgementand may not require an STA other than the RD Initiator to send a blockacknowledgement, a conflict occurring between a case where the RDInitiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder does notoccur.

BRIEF DESCRIPTION OF THE DRAWINGS

To illustrate the technical solutions in the embodiments of the presentinvention more clearly, the accompanying drawings required fordescribing the embodiments are briefly described in the following.Apparently, the accompanying drawings in the following descriptionmerely show some embodiments of the present invention, and persons ofordinary skill in the art may still derive other drawings from theseaccompanying drawings.

FIG. 1 is a flow chart of a method for retrieving transmissionopportunity control in reverse direction grant according to anembodiment of the present invention;

FIG. 2 is a schematic diagram of frame interaction between an RDInitiator and an RD Responder according to an embodiment of the presentinvention;

FIG. 3 is a flow chart of a method for retrieving transmissionopportunity control in reverse direction grant according to anotherembodiment of the present invention;

FIG. 4 is a schematic diagram of a reverse direction initiator accordingto an embodiment of the present invention; and

FIG. 5 is a schematic diagram of a reverse direction initiator accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention provide a method and an apparatusfor retrieving transmission opportunity control in reverse directiongrant, so that a conflict occurring between a case where an RD Initiatorcontinues sending another frame to an RD Responder after retrieving TXOPcontrol and a case where a terminal other than the RD Initiator sends ablock acknowledgement to the RD Responder can be avoided.

To make the objectives, features, and advantages of the presentinvention clearer and more comprehensible, the technical solutions inthe embodiments of the present invention are described clearly andcompletely in the following with reference to the accompanying drawingsin the embodiments of the present invention. Apparently, the embodimentsto be described are only a part rather than all of the embodiments ofthe present invention. Based on the embodiments of the presentinvention, all other embodiments derived by persons skilled in the artshall fall within the protection scope of the present invention.

An embodiment of the present invention provides a method for retrievingTXOP control in RDG, where the method includes:

when an RD Initiator fails to correctly demodulate a frame sent by an RDResponder, retrieving, by the RD Initiator, TXOP control by using a PIFSif it is impossible for the RD Responder to enable an MU-MIMO mode, andretrieving, by the RD Initiator, the TXOP control by using a duration ifit is possible for the RD Responder to enable the MU-MIMO mode, wherethe duration is longer than the PIFS.

In this embodiment of the present invention, when the RD Initiator failsto correctly demodulate the frame sent by the RD Responder, the RDInitiator retrieves the TXOP control by using a duration if it ispossible for the RD Responder to enable the MU-MIMO mode, where theduration is longer than the PIFS. Because the RD Initiator retrieves theTXOP control by using a duration that is longer than the PIFS, that is,within the duration that is longer than the PIFS, a terminal other thanthe RD Initiator sends a block acknowledgment to the RD Responder, andthen the RD Responder continues sending a frame. In this case, the RDInitiator may intercept that a channel is in a busy state, and does notretrieve the TXOP control, thereby avoiding a conflict occurring betweena case where the RD Initiator continues sending another frame to the RDResponder after retrieving the TXOP control and a case where theterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder. If it is impossible for the RD Responder to enable theMU-MIMO mode, it is impossible for the RD Responder to concurrently senda frame to the RD Initiator and the terminal other than the RDInitiator. Therefore, a conflict between a case where the RD Initiatorcontinues sending another frame to the RD Responder after retrieving theTXOP control and a case where the terminal other than the RD Initiatorsends a block acknowledgement to the RD Responder does not occur.

For details of the method for retrieving TXOP control in RDG provided inthis embodiment of the present invention, reference is made to FIG. 1.The method for retrieving TXOP control in RDG provided in thisembodiment of the present invention includes:

101. When an RD Initiator fails to correctly demodulate a frame sent byan RD Responder, the RD Initiator determines whether it is possible forthe RD Responder to enable an MU-MIMO mode. If it is impossible for theRD Responder to enable the MU-MIMO mode, 102 is triggered for execution;and if it is possible for the RD Responder to enable the MU-MIMO mode,103 is triggered for execution.

In this embodiment of the present invention, in a scenario where the RDInitiator fails to correctly demodulate the frame sent by the RDResponder, the RD Initiator determines whether it is possible for the RDResponder to enable the MU-MIMO mode. It should be noted that there aremultiple implementation manners for the RD Initiator to determinewhether it is possible for the RD Responder to enable the MU-MIMO mode.The following describes the multiple implementation modes in detail.

A1. The RD Initiator determines whether the RD Initiator supports theMU-MIMO mode. If the RD Initiator does not support the MU-MIMO mode, itis impossible for the RD Responder to enable the MU-MIMO mode.

A frame is transmitted between the RD Initiator and the RD Responder. Ifthe RD Initiator does not support the MU-MIMO mode, it is impossible forthe RD Responder to enable the MU-MIMO mode.

A2. The RD Initiator determines whether the RD Initiator belongs to anygroup that is used for enabling the MU-MIMO mode. If the RD Initiatordoes not belong to any group that is used for enabling the MU-MIMO mode,it is impossible for the RD Responder to enable the MU-MIMO mode.

A frame is transmitted between the RD Initiator and the RD Responder. Ifthe RD Initiator does not belong to any group (Group) that is used forenabling the MU-MIMO mode, it is impossible for the RD Responder toenable the MU-MIMO mode.

A3. The RD Initiator determines whether the RD Responder supports theMU-MIMO mode. If the RD Responder does not support the MU-MIMO mode, itis impossible for the RD Responder to enable the MU-MIMO mode.

Before a frame is transmitted between the RD Initiator and the RDResponder, the RD Initiator is capable of acquiring whether the RDResponder supports the MU-MIMO mode. If the RD Responder does notsupport the MU-MIMO mode, it is impossible for the RD Responder toenable the MU-MIMO mode.

It should be noted that, for the foregoing three implementation mannersA1, A2, and A3, if at least one of three determination results is “no”,the RD Initiator may determine that it is impossible for the RDResponder to enable the MU-MIMO mode, and 102 is triggered forexecution. The foregoing A1, A2, and A3 are all optional determinationmethods and any one of them may be selected. Alternatively, personsskilled in the art may use other determination methods. Thedetermination methods herein are for illustration only rather thanlimitation.

On the contrary, when the RD Initiator belongs to at least one groupthat is used for enabling the MU-MIMO mode, the RD Initiator mayconsider that it is possible for the RD Responder to enable the MU-MIMOmode, and 103 is triggered for execution. Definitely, otherimplementation manners may also be used for determining that it ispossible for the RD Responder to enable the MU-MIMO mode. Theimplementation manners herein are for illustration only rather thanlimitation.

102. If it is impossible for the RD Responder to enable the MU-MIMOmode, the RD Initiator retrieves TXOP control by using a PIFS.

In this embodiment of the present invention, if it is impossible for theRD Responder to enable the MU-MIMO mode, the RD Responder is capable ofsending a frame to only the RD Initiator, but is incapable of sending aframe to an STA other than the RD Initiator, and may also not requirethe STA other than the RD Initiator to send a block acknowledgement. Inthis case, the RD Initiator retrieves the TXOP control by using thePIFS, and then continues sending another frame to the RD Responder.Therefore, a conflict between a case where the RD Initiator continuessending another frame to the RD Responder after retrieving the TXOPcontrol and a case where the terminal other than the RD Initiator sendsa block acknowledgement to the RD Responder does not occur.

In this embodiment of the present invention, retrieving the TXOP controlby using the PIFS means that when the RD Initiator fails to correctlydemodulate a frame, and does not know whether the frame is a last frameand whether a block acknowledgement is needed for the frame, within onePIFS, the RD Initiator intercepts a state of a channel (busy or idle).If the channel is in an idle state within the PIFS, the RD Initiatorretrieves the TXOP control. One PIFS is one short inter-frame space plusone time slot.

In a BSS network, only one central station for dedicatedly managing theBSS is called an access point (AP, Access Point), whereas other stationsthat are not an AP are called terminals, or called non-AP STAs. The APand non-AP STAs are collectively called STAs. The AP and non-AP STAs donot need to be distinguished in description of the STA.

For an independent BSS network, a direct data transmission object of anSTA is another STA. For a BSS network that has an AP, a direct datatransmission object of a non-AP STA is another non-AP STA or AP.However, in one BSS network, a direct data transmission object of an APmay be a plurality of non-AP STAs. Therefore, when an AP obtains TXOPcontrol, within one control period of TXOP control, a direct datatransmission object of the AP may be a plurality of non-AP STAs. Whenthe AP serves as an RD Responder but it is impossible for the RDResponder to enable an MU-MIMO mode, the RD Initiator retrieves the TXOPcontrol by using a PIFS, and therefore, a conflict between a case wherethe RD Initiator continues sending another frame to the RD Responderafter retrieving the TXOP control and a case where the terminal otherthan the RD Initiator sends a block acknowledgement to the RD Responderdoes not occur.

103. If it is possible for the RD Responder to enable the MU-MIMO mode,the RD Initiator retrieves the TXOP control by using a duration that islonger than the PIFS.

In this embodiment of the present invention, it can be known through thedetermination in 101 that when it is possible for the RD Responder toenable the MU-MIMO mode, the RD Initiator retrieves the TXOP control byusing a duration that is longer than the PIFS.

In this embodiment of the present invention, retrieving the TXOP controlby using a duration that is longer than the PIFS means that when the RDInitiator fails to correctly demodulate a frame, and does not knowwhether the frame is a last frame and whether a block acknowledgement isneeded for the frame, within one duration that is longer than the PIFS,the RD Initiator intercepts a state of a channel (busy or idle). If thechannel is in an idle state within the duration that is longer than thePIFS, the RD Initiator retrieves the TXOP control.

It should be noted that in this embodiment of the present invention, ina practical application, the duration that is longer than the PIFS maybe implemented in multiple implementation manners. The followingdescribes the multiple implementation manners in detail.

One implementation manner is that the duration that is longer than thePIFS may be expressed as the following expression (1):

Duration that is longer than the PIFS=2*SIFS+aSlotTime+Max(BA Time),

where the SIFS is a short inter-frame space, the aSlotTime is aninterval, and the Max(BA Time) is a maximum duration for sending a blockacknowledgement frame. The maximum duration for sending a blockacknowledgement frame is a duration required for modulating the blockacknowledgement frame at a minimum bit rate and separately sending theblock acknowledgement frame by using a minimum unit frequency band.

It can be obtained from the expression (1) that within the duration thatis longer than the PIFS and is described in the expression (1), if aterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder, the RD Initiator is capable of intercepting on achannel that the channel is in a busy state, and does not retrieve theTXOP control, thereby avoiding a conflict occurring between a case wherethe RD Initiator continues sending another frame to the RD Responderafter retrieving the TXOP control and a case where the terminal otherthan the RD Initiator sends a block acknowledgement to the RD Responder.

Another implementation manner is that a block acknowledgement frame sentby an STA other than the RD Initiator is a compressed blockacknowledgement frame (Compressed BA), the duration that is longer thanthe PIFS may be expressed as the following expression (2):

Duration that is longer than the PIFS=2*SIFS+aSlotTime+Max(Compressed BATime),

where the SIFS is a short inter-frame space, the aSlotTime is aninterval, and the Max(Compressed BA Time) is a maximum duration forsending a compressed block acknowledgement frame. The maximum durationfor sending a compressed block acknowledgement frame is a duration formodulating the block acknowledgement frame at a minimum bit rate andseparately sending the block acknowledgement frame by using a minimumunit frequency band.

It can be obtained from the expression (2) that within the duration thatis longer than the PIFS and is described in the expression (2), if aterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder, the RD Initiator is capable of intercepting on achannel that the channel is in a busy state, and does not retrieve theTXOP control, thereby avoiding a conflict occurring between a case wherethe RD Initiator continues sending another frame to the RD Responderafter retrieving the TXOP control and a case where the terminal otherthan the RD Initiator sends a block acknowledgement to the RD Responder.

In this embodiment of the present invention, when the RD Initiator failsto correctly demodulate the frame sent by the RD Responder, the RDInitiator retrieves the TXOP control by using a duration if it ispossible for the RD Responder to enable the MU-MIMO mode, where theduration is longer than the PIFS. Because the RD Initiator retrieves theTXOP control by using a duration that is longer than the PIFS, that is,within the duration that is longer than the PIFS, a terminal other thanthe RD Initiator sends a block acknowledgment to the RD Responder, andthen the RD Responder continues sending a frame. In this case, the RDInitiator may intercept that a channel is in a busy state, and does notretrieve the TXOP control, thereby avoiding a conflict occurring betweena case where the RD Initiator continues sending another frame to the RDResponder after retrieving the TXOP control and a case where theterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder. If it is impossible for the RD Responder to enable theMU-MIMO mode, it is impossible for the RD Responder to concurrently senda frame to the RD Initiator and the terminal other than the RDInitiator. Therefore, a conflict between a case where the RD Initiatorcontinues sending another frame to the RD Responder after retrieving theTXOP control and a case where the terminal other than the RD Initiatorsends a block acknowledgement to the RD Responder does not occur.

A method for retrieving transmission opportunity control in reversedirection grant provided in an embodiment of the present invention isdescribed in the following by using a detailed application scenario. Asshown in FIG. 2, in a BSS network, an AP, an STA1, an STA2, and an STA3exist. The STA1 first obtains TXOP control through contention, and theSTA1 becomes a TXOP holder. The STA1 sends a frame 1 and a frame 2 tothe AP. When the TXOP holder does not transmit data itself, the TXOPholder temporarily transfers the TXOP control to the AP to enable the APto send data to the TXOP holder. That is, the STA1 is an RD Initiator,and the AP is an RD Responder.

As shown in FIG. 2, within one TXOP, after sending the frame 1 to theAP, the STA1 requires the AP to send an acknowledgement. The AP sends aBA1 to the STA1, and then the STA1 sends the frame 2 to the AP andtemporarily transfers the TXOP control to the AP. Within an RDG MU-MIMOtransmission duration, the AP sends a frame 5 to the STA1. Because theAP enables an MU-MIMO mode, the AP concurrently sends the frame 5 to theSTA2 and a frame 3 to the STA3, and requires the STA2 to send anacknowledgement. Therefore, the STA2 sends a BA2 to the AP. In thiscase, demodulation of the STA1 on the frame 5 fails, that is, the STA1fails to correctly demodulate the frame 5. According to the methodprovided in this embodiment of the present invention, when the STA1 thatservers as the RD Initiator fails to correctly demodulate a frame sentby the RD Responder, the RD Initiator determines whether it is possiblefor the RD Responder (that is, the AP) to enable the MU-MIMO mode. If itis possible for the RD Responder to enable the MU-MIMO mode, the RDInitiator retrieves the TXOP control by using a duration that is longerthan a PIFS. In an embodiment illustrated in FIG. 2, when the RDInitiator intercepts a busy/idle state of a channel within the durationthat is longer than the PIFS, and finds that the channel is in the busystate (the channel is in the busy state because the STA2 sends the BA2to the AP). Therefore, the STA1 does not retrieve the TXOP control.

After receiving the BA2 sent by the STA2, the AP sends a BAR1 to theSTA3, to require the STA3 to send an acknowledgement. Therefore, theSTA3 sends a BA3 to the STA1 according to a requirement of the AP. Then,the AP continues sending a frame 8 to the STA1, and concurrently sends aframe 7 to the STA2 and a frame 6 to the STA3. After sending the threeframes, the AP completes frame sending. In this case, the AP sends aBRA2 to the STA1, to require the STA1 to send an acknowledgement.However, when the STA1 fails to correctly demodulate the BAR2, accordingto the method provided in this embodiment of the present invention, theRD Initiator retrieves the TXOP control by using the PIFS if it isimpossible for the RD Responder to enable the MU-MIMO mode. That is, ifthe STA1 intercepts within the PIFS that the channel is always in theidle state, the STA1 may retrieve the TXOP control. According to themethod provided in this embodiment of the present invention, if it ispossible for the RD Responder to enable the MU-MIMO mode, the RDInitiator retrieves the TXOP control by using a duration that is longerthan the PIFS. That is, if the STA1 intercepts within the duration thatis longer than the PIFS that the channel is always in the idle state,the STA1 may retrieve the TXOP control and then continues sending aframe 9 to the AP.

Another method for retrieving TXOP control in RDG provided in anembodiment of the present invention is described in the following, andincludes:

when an RD Initiator fails to correctly demodulate a very highthroughput signaling A1 in a frame sent by an RD responder, retrieving,by the RD Initiator, TXOP control by using a PIFS if it is impossiblefor the RD Responder to enable an MU-MIMO mode, and retrieving, by theRD Initiator, the TXOP control by using a duration if it is possible forthe RD Responder to enable the MU-MOMO mode, where the duration islonger than the PIFS;

when the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, retrieving, by the RDInitiator, the TXOP control by using the PIFS if the frame is asingle-user frame and a value of a Partial AID in the very highthroughput signaling A1 is the same as a value of a Partial AID of theRD Initiator;

when the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, retrieving, by the RDInitiator, the TXOP control by using a duration if the frame is amulti-user frame, where the duration is longer than the PIFS; and

when the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, retrieving, by the RDInitiator, the TXOP control by using a duration if the frame is asingle-user frame and the value of the Partial AID in the very highthroughput signaling A1 is different from the value of the Partial AIDof the RD Initiator, where the duration is longer than the PIFS.

In another embodiment of the present invention, when an RD Initiatorfails to correctly demodulate a very high throughput signaling A1 in aframe sent by an RD responder, the RD Initiator retrieves TXOP controlby using a duration if it is possible for the RD Responder to enable anMU-MIMO mode, where the duration is longer than a PIFS. Because the RDInitiator retrieves the TXOP control by using a duration that is longerthan the PIFS, that is, within the duration that is longer than thePIFS, a terminal other than the RD Initiator sends a blockacknowledgment to the RD Responder, and then the RD Responder continuessending a frame. In this case, the RD Initiator may intercept that achannel is in a busy state, and does not retrieve the TXOP control,thereby avoiding a conflict occurring between a case where the RDInitiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder.

When the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, the RD Initiator retrievesthe TXOP control by using the PIFS if the frame is a single-user frameand a value of a Partial AID in the frame is the same as a value of aPartial AID of the RD Initiator. Because the frame sent by the RDResponder to the RD Initiator is a single-user frame, that is, the frameis sent only by the RD Responder to the RD Initiator, it is impossiblefor the RD Responder to concurrently send a frame to the RD Initiatorand the terminal other than the RD Initiator. Therefore, a conflictbetween a case where the RD Initiator continues sending another frame tothe RD Responder after retrieving the TXOP control and a case where theterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder does not occur.

When the RD Initiator satisfies one of the following conditions, the RDInitiator retrieves the TXOP control by using a duration that is longerthan the PIFS. Preset conditions are: The frame is a multi-user frame;and the value of the Partial AID in the very high throughput signalingA1 is different from the value of the Partial AID of the RD Initiator.Because the RD Initiator retrieves the TXOP control by using a durationthat is longer than the PIFS, that is, within the duration that islonger than the PIFS, a terminal other than the RD Initiator sends ablock acknowledgment to the RD Responder, and then the RD Respondercontinues sending a frame. In this case, the RD Initiator may interceptthat a channel is in a busy state, and does not retrieve the TXOPcontrol, thereby avoiding a conflict occurring between a case where theRD Initiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder.

For details of the method for retrieving TXOP control in RDG provided inthis embodiment of the present invention, reference is made to FIG. 3,where the method includes:

301. An RD Initiator demodulates a very high throughput signaling A1 ina frame sent by an RD Responder. If the RD Initiator fails to correctlydemodulate the very high throughput signaling A1, 302 is triggered forexecution; and if the RD Initiator correctly demodulates the very highthroughput signaling A1 but fails to correctly demodulate the framecompletely, 304 is triggered for execution.

In this embodiment of the present invention, the RD Initiatordemodulates the very high throughput signaling A1 in the frame, wherethe very high throughput signaling A1 (Very high Throughput Signalfield-A1, VH-SIG-A1) carries a group identifier (Group Identifier, GroupID) and a partial association identifier (Partial associationidentifier, Partial AID).

302. When the RD Initiator fails to correctly demodulate the very highthroughput signaling A1 in the frame sent by the RD Responder, the RDInitiator determines whether it is possible for the RD Responder toenable an MU-MIMO mode. If it is impossible for the RD Responder toenable the MU-MIMO mode, 303 is triggered for execution; and if it ispossible for the RD Responder to enable the MU-MIMO mode, 306 istriggered for execution.

In this embodiment of the present invention, in a scenario where the RDInitiator fails to correctly demodulate the very high throughputsignaling A1 in the frame sent by the RD Responder, the RD Initiatordetermines whether it is possible for the RD Responder to enable theMU-MIMO mode. It should be noted that there are multiple implementationmanners for the RD Initiator to determine whether it is possible for theRD Responder to enable the MU-MIMO mode. The following describes themultiple implementation manners in detail.

B1. The RD Initiator determines whether the RD Initiator supports theMU-MIMO mode. If the RD Initiator does not support the MU-MIMO mode, itis impossible for the RD Responder to enable the MU-MIMO mode.

A frame is transmitted between the RD Initiator and the RD Responder. Ifthe RD Initiator does not support the MU-MIMO mode, it is impossible forthe RD Responder to enable the MU-MIMO mode.

B2. The RD Initiator determines whether the RD Initiator belongs to anygroup that is used for enabling the MU-MIMO mode. If the RD Initiatordoes not belong to any group that is used for enabling the MU-MIMO mode,it is impossible for the RD Responder to enable the MU-MIMO mode.

A frame is transmitted between the RD Initiator and the RD Responder. Ifthe RD Initiator does not belong to any group (Group) that is used forenabling the MU-MIMO mode, it is impossible for the RD Responder toenable the MU-MIMO mode.

B3. The RD Initiator determines whether the RD Responder supports theMU-MIMO mode. If the RD Responder does not support the MU-MIMO mode, itis impossible for the RD Responder to enable the MU-MIMO mode.

Before a frame is transmitted between the RD Initiator and the RDResponder, the RD Initiator is capable of acquiring whether the RDResponder supports the MU-MIMO mode. If the RD Responder does notsupport the MU-MIMO mode, it is impossible for the RD Responder toenable the MU-MIMO mode.

It should be noted that, for the foregoing three implementation mannersB1, B2, and B3, if at least one of three determination results is “no”,the RD Initiator may determine that it is impossible for the RDResponder to enable the MU-MIMO mode, and 302 is triggered forexecution. The foregoing B1, B2, and B3 are all optional determinationmethods and any one of them may be selected. Alternatively, personsskilled in the art may use other determination methods. Thedetermination methods herein are for illustration only rather thanlimitation.

On the contrary, when the RD Initiator belongs to at least one groupthat is used for enabling the MU-MIMO mode, the RD Initiator mayconsider that it is possible for the RD Responder to enable the MU-MIMOmode, and 303 is triggered for execution. Definitely, otherimplementation manners may also be used for determining that it ispossible for the RD Responder to enable the MU-MIMO mode. Theimplementation manners herein are for illustration only rather thanlimitation.

303. The RD Initiator retrieves TXOP control by using a PIFS.

In this embodiment of the present invention, if it is impossible for theRD Responder to enable the MU-MIMO mode, the RD Responder is capable ofsending a frame to only the RD Initiator, but is incapable of sending aframe to an STA other than the RD Initiator, and may also not requirethe STA other than the RD Initiator to send a block acknowledgement. Inthis case, the RD Initiator retrieves the TXOP control by using thePIFS, and then continues sending another frame to the RD Responder.Therefore, a conflict between a case where the RD Initiator continuessending another frame to the RD Responder after retrieving the TXOPcontrol and a case where the terminal other than the RD Initiator sendsa block acknowledgement to the RD Responder does not occur.

304. If the RD Initiator correctly demodulates the very high throughputsignaling A1 and the RD Initiator determines, according to the groupidentifier in the very high throughput signaling A1, whether the frameis a single-user frame. If the frame is a single-user frame, 305 istriggered for execution; and if the frame is not a single-user frame,306 is triggered for execution.

In a very high throughput signaling A1 (VHT-SIG-A1, Very HighThroughput-Signal-A1) at a physical layer, a group identifier (Group ID)field is used to indicate MU-MIMO, and a partial association identifier(Partial AID) field is used to indicate an ID of a target STA of thedata. When a value of the Group ID field is a value ranging from 2 to62, it indicates that the data packet is a multi-user (Multiple-User)data packet; and when the value of the Group ID field is 0 or 63, itindicates that the data packet is a single-user (SU, Single User) datapacket. If a value of the Partial AID field in the data packet matcheswith that of a Partial AID of an STA, it indicates that the SU datapacket is a data packet of the STA.

In this embodiment of the present invention, the RD Initiatordetermines, according to the group identifier in the very highthroughput signaling A1, whether the frame is a single-user frame, whichmay specifically be: determining whether a value of a Group ID is 0 or63. If the value of the Group ID is 0 or 63, the frame is a single-userframe. If the value of the Group ID is neither 0 nor 63, the frame isnot a single-user frame but is a multi-user frame.

305. If the frame is a single-user frame, the RD Initiator determineswhether a value of a Partial AID in the frame is the same as a value ofa Partial AID of the RD Initiator. If the value of the Partial AID inthe frame is the same as the value of the Partial AID of the RDInitiator, 302 is triggered for execution. If the value of the PartialAID in the frame is different from the value of the Partial AID of theRD Initiator, 306 is triggered for execution.

306. The RD Initiator retrieves the TXOP control by using a durationthat is longer than the PIFS.

It should be noted that 306 in the embodiment illustrated in FIG. 3 issimilar to 103 shown in FIG. 1, which is not detailed here again.

It should be noted that in this embodiment of the present invention, ina practical application, the duration that is longer than the PIFS maybe implemented in multiple implementation manners. The followingdescribes the multiple implementation manners in detail.

One implementation manner is that, within the duration that is longerthan the PIFS and is described in the expression (1), if a terminalother than the RD Initiator sends a block acknowledgement to the RDResponder, the RD Initiator is capable of intercepting on a channel thatthe channel is in a busy state, and does not retrieve the TXOP control,thereby avoiding a conflict occurring between a case where the RDInitiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder.

Another implementation manner is that, within the duration that islonger than the PIFS and is described in the expression (2), if aterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder, the RD Initiator is capable of intercepting on achannel that the channel is in a busy state, and does not retrieve theTXOP control, thereby avoiding a conflict occurring between a case wherethe RD Initiator continues sending another frame to the RD Responderafter retrieving the TXOP control and a case where the terminal otherthan the RD Initiator sends a block acknowledgement to the RD Responder.

In this embodiment of the present invention, when the RD Initiator failsto correctly demodulate the very high throughput signaling in the framesent by the RD responder, the RD Initiator retrieves the TXOP control byusing a duration if it is possible for the RD Responder to enable theMU-MIMO mode, where the duration is longer than the PIFS. Because the RDInitiator retrieves the TXOP control by using a duration that is longerthan the PIFS, that is, within the duration that is longer than thePIFS, a terminal other than the RD Initiator sends a blockacknowledgment to the RD Responder, and then the RD Responder continuessending a frame. In this case, the RD Initiator may intercept that achannel is in a busy state, and does not retrieve the TXOP control,thereby avoiding a conflict occurring between a case where the RDInitiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder.

When the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, the RD Initiator retrievesthe TXOP control by using the PIFS if the frame is a single-user frameand the value of the Partial AID in the frame is the same as the valueof the Partial AID of the RD Initiator. Because the frame sent by the RDResponder to the RD Initiator is a single-user frame, that is, the frameis sent only by the RD Responder to the RD Initiator, it is impossiblefor the RD Responder to concurrently send a frame to the RD Initiatorand the terminal other than the RD Initiator. Therefore, a conflictbetween a case where the RD Initiator continues sending another frame tothe RD Responder after retrieving the TXOP control and a case where theterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder does not occur.

When the RD Initiator satisfies one of the following conditions, the RDInitiator retrieves the TXOP control by using a duration that is longerthan the PIFS. The following conditions are: The frame is not asingle-user frame; and the value of the Partial AID in the very highthroughput signaling A1 is different from the value of the Partial AIDof the RD Initiator. Because the RD Initiator retrieves the TXOP controlby using a duration that is longer than the PIFS, that is, within theduration that is longer than the PIFS, a terminal other than the RDInitiator sends a block acknowledgment to the RD Responder, and then theRD Responder continues sending a frame. In this case, the RD Initiatormay intercept that a channel is in a busy state, and does not retrievethe TXOP control, thereby avoiding a conflict occurring between a casewhere the RD Initiator continues sending another frame to the RDResponder after retrieving the TXOP control and a case where theterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder.

Another method for retrieving transmission opportunity control inreverse direction grant provided in an embodiment of the presentinvention is described in the following, and includes:

when an RD responder enables an MU-MIMO mode, and the RD responderconcurrently sends a frame to a plurality of stations that include an RDInitiator, requiring only the RD Initiator to send a blockacknowledgement, so that the RD Initiator is capable of retrieving TXOPcontrol.

In a practical application, the method may further include: when the RDInitiator fails to correctly demodulate the frame sent by the RDResponder, retrieving, by the RD Initiator, the TXOP control by using aPIFS.

In this embodiment of the present invention, when the RD responderenables the MU-MIMO mode, and concurrently sends a frame to a pluralityof stations that include the RD Initiator, only the RD Initiator isrequired to send a block acknowledgement, so that the RD Initiator iscapable of retrieving the TXOP control. The RD Responder requires onlythe RD Initiator to send a block acknowledgement. Because the RDResponder may not require an STA other than the RD Initiator to send ablock acknowledgement. Therefore, a conflict between a case where the RDInitiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder does notoccur.

In the foregoing embodiments, the method for retrieving transmissionopportunity control in reverse direction grant provided in theembodiments of the present invention is described. A reverse directioninitiator RD Initiator provided in an embodiment of the presentinvention is described in the following.

As shown in FIG. 4, an embodiment of the present invention provides areverse direction initiator RD Initiator 400, including:

a first control retrieving unit 401, configured to, when an RD Initiatorfails to correctly demodulate a frame sent by an RD Responder, retrieveTXOP control by using a PIFS if it is impossible for the RD Responder toenable an MU-MIMO mode;

a second control retrieving unit 402, configured to, when the RDInitiator fails to correctly demodulate the frame sent by the RDResponder, retrieve the TXOP control by using a duration if it ispossible for the RD Responder to enable the MU-MIMO mode, where theduration is longer than the PIFS.

For the first control retrieving unit 401, in a practical application,an implementable manner is that the first control retrieving unit 401 isspecifically configured to:

retrieve the TXOP control by using the PIFS when the RD Initiator failsto correctly demodulate the frame sent by the RD Responder and the RDInitiator does not support the MU-MIMO mode;

or

retrieve the TXOP control by using the PIFS when the RD Initiator failsto correctly demodulate the frame sent by the RD Responder and the RDInitiator does not belong to any group that is used for enabling theMU-MIMO mode;

or

retrieve the TXOP control by using the PIFS when the RD Initiator failsto correctly demodulate the frame sent by the RD Responder and the RDResponder does not support the MU-MIMO mode.

For the second control retrieving unit 402, in a practical application,an implementable manner is that the second control retrieving unit 402is specifically configured to:

retrieve the TXOP control by using a duration when the RD Initiatorfails to correctly demodulate the frame sent by the RD Responder and theRD Initiator belongs to at least one group that is used for enabling theMU-MIMO mode, where the duration is longer than the PIFS.

It should be noted that content such as information exchange and anexecution process between modules/units of the apparatus is based on thesame concept as the method embodiments of the present invention. Thetechnical effects are the same as those of the method embodiments of thepresent invention. For details, reference may be made to the descriptionof the method embodiment illustrated in FIG. 1 in the present invention,which are not detailed here again.

In this embodiment of the present invention, if it is possible for theRD Responder to enable the MU-MIMO mode, the second control retrievingunit 402 retrieves the TXOP control by using a duration that is longerthan the PIFS. Because the RD Initiator retrieves the TXOP control byusing a duration that is longer than the PIFS, within the duration thatis longer than the PIFS, a terminal other than the RD Initiator sends ablock acknowledgment to the RD Responder, and then the RD Respondercontinues sending a frame. In this case, the RD Initiator may interceptthat a channel is in a busy state, and does not retrieve the TXOPcontrol, thereby avoiding a conflict occurring between a case where theRD Initiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder. If it isimpossible for the RD Responder to enable the MU-MIMO mode, it isimpossible for the RD Responder to concurrently send a frame to the RDInitiator and the terminal other than the RD Initiator. Therefore, aconflict between a case where the RD Initiator continues sending anotherframe to the RD Responder after retrieving the TXOP control and a casewhere the terminal other than the RD Initiator sends a blockacknowledgement to the RD Responder does not occur.

As shown in FIG. 5, an embodiment of the present invention providesanother reverse direction initiator 500, including:

a first control retrieving unit 501, configured to, when an RD Initiatorfails to correctly demodulate a very high throughput signaling A1 in aframe sent by an RD Responder, retrieve TXOP control by using a PIFS ifit is impossible for the RD Responder to enable an MU-MIMO mode;

a second control retrieving unit 502, configured to, when the RDInitiator fails to correctly demodulate the very high throughputsignaling A1 in the frame sent by the RD Responder, retrieve the TXOPcontrol by using a duration if it is possible for the RD Responder toenable the MU-MIMO mode, where the duration is longer than the PIFS;

a third control retrieving unit 503, configured to, when the RDInitiator correctly demodulates the very high throughput signaling A1 inthe frame sent by the RD responder but fails to correctly demodulate theframe completely, retrieve the TXOP control by using the PIFS if theframe is a single-user frame and a value of a Partial AID in the veryhigh throughput signaling A1 is the same as a value of a Partial AID ofthe RD Initiator;

a fourth control retrieving unit 504, configured to, when the RDInitiator correctly demodulates the very high throughput signaling A1 inthe frame sent by the RD responder but fails to correctly demodulate theframe completely, retrieve the TXOP control by using a duration if theframe is a multi-user frame, where the duration is longer than the PIFS;and

a fifth control retrieving unit 505, configured to, when the RDInitiator correctly demodulates the very high throughput signaling A1 inthe frame sent by the RD responder but fails to correctly demodulate theframe completely, retrieve the TXOP control by using a duration if theframe is a single-user frame and the value of the Partial AID in thevery high throughput signaling A1 is different from the value of thePartial AID of the RD Initiator, where the duration is longer than thePIFS.

For the first control retrieving unit 501, in a practical application,an implementable manner is that the first control retrieving unit 501 isspecifically configured to:

retrieve the TXOP control by using the PIFS when the RD Initiator failsto correctly demodulate the frame sent by the RD Responder and the RDInitiator does not support the MU-MIMO mode;

or

retrieve the TXOP control by using the PIFS when the RD Initiator failsto correctly demodulate the frame sent by the RD Responder and the RDInitiator does not belong to any group that is used for enabling theMU-MIMO mode;

or

retrieve the TXOP control by using the PIFS when the RD Initiator failsto correctly demodulate the frame sent by the RD Responder and the RDResponder does not support the MU-MIMO mode.

For the second control retrieving unit 502, in a practical application,an implementable manner is that the second control retrieving unit 502is specifically configured to:

retrieve the TXOP control by using a duration when the RD Initiatorfails to correctly demodulate the frame sent by the RD Responder and theRD Initiator belongs to at least one group that is used for enabling theMU-MIMO mode, where the duration is longer than the PIFS.

It should be noted that content such as information exchange and anexecution process between modules/units of the apparatus is based on thesame concept as the method embodiments of the present invention. Thetechnical effects are the same as those of the method embodiments of thepresent invention. For details, reference may be made to the descriptionof the method embodiment illustrated in FIG. 3 in the present invention,which are not detailed here again.

In this embodiment of the present invention, when the RD Initiator failsto correctly demodulate the very high throughput signaling Al in theframe sent by the RD responder, the RD Initiator retrieves the TXOPcontrol by using a duration if it is possible for the RD Responder toenable the MU-MIMO mode, where the duration is longer than the PIFS.Because the RD Initiator retrieves the TXOP control by using a durationthat is longer than the PIFS, that is, within the duration that islonger than the PIFS, a terminal other than the RD Initiator sends ablock acknowledgment to the RD Responder, and then the RD Respondercontinues sending a frame. In this case, the RD Initiator may interceptthat a channel is in a busy state, and does not retrieve the TXOPcontrol, thereby avoiding a conflict occurring between a case where theRD Initiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder.

When the RD Initiator correctly demodulates the very high throughputsignaling A1 in the frame sent by the RD responder but fails tocorrectly demodulate the frame completely, the RD Initiator retrievesthe TXOP control by using the PIFS if the frame is a single-user frameand the value of the Partial AID in the frame is the same as the valueof the Partial AID of the RD Initiator. Because the frame sent by the RDResponder to the RD Initiator is a single-user frame, that is, the frameis sent only by the RD Responder to the RD Initiator, it is impossiblefor the RD Responder to concurrently send a frame to the RD Initiatorand the terminal other than the RD Initiator. Therefore, a conflictbetween a case where the RD Initiator continues sending another frame tothe RD Responder after retrieving the TXOP control and a case where theterminal other than the RD Initiator sends a block acknowledgement tothe RD Responder does not occur.

When the RD Initiator satisfies one of the following conditions, the RDInitiator retrieves the TXOP control by using a duration that is longerthan the PIFS. The following conditions are: The frame is a multi-userframe; and the value of the Partial AID in the very high throughputsignaling A1 is different from the value of the Partial AID of the RDInitiator. Because the RD Initiator retrieves the TXOP control by usinga duration that is longer than the PIFS, that is, within the durationthat is longer than the PIFS, a terminal other than the RD Initiatorsends a block acknowledgment to the RD Responder, and then the RDResponder continues sending a frame. In this case, the RD Initiator mayintercept that a channel is in a busy state, and does not retrieve theTXOP control, thereby avoiding a conflict occurring between a case wherethe RD Initiator continues sending another frame to the RD Responderafter retrieving the TXOP control and a case where the terminal otherthan the RD Initiator sends a block acknowledgement to the RD Responder.

A reverse direction responder RD Responder provided in an embodiment ofthe present invention is described in the following. An RD Responder isconfigured to, when the RD responder enables an MU-MIMO mode, andconcurrently sends a frame to a plurality of stations that include an RDInitiator, require only the RD Initiator to send a blockacknowledgement, so that the RD Initiator is capable of retrieving TXOPcontrol.

In this case, when the RD Initiator fails to correctly demodulate aframe sent by the RD Responder, the RD Initiator retrieves the TXOPcontrol by using a PIFS.

In this embodiment of the present invention, when the RD responderenables the MU-MIMO mode, and concurrently sends a frame to a pluralityof stations that include the RD Initiator, only the RD Initiator isrequired to send a block acknowledgement, so that the RD Initiator iscapable of retrieving the TXOP control. Because the RD Responderrequires only the RD Initiator to send a block acknowledgement and maynot require an STA other than the RD Initiator to send a blockacknowledgement. Therefore, a conflict between a case where the RDInitiator continues sending another frame to the RD Responder afterretrieving the TXOP control and a case where the terminal other than theRD Initiator sends a block acknowledgement to the RD Responder does notoccur.

Persons of ordinary skill in the art may understand that all or a partof the steps of the methods in the embodiments may be implemented by aprogram instructing relevant hardware. The program may be stored in acomputer readable storage medium. The storage medium may be a read-onlymemory, a magnetic disk, or an optical disk, and the like.

The method and the apparatus for retrieving transmission opportunitycontrol in reverse direction grant provided in the present invention aredescribed in detail in the foregoing. Persons of ordinary skill in theart may make variations to the specific implementation manner andapplication scope according to the ideas of the embodiments of thepresent invention. In conclusion, the content of this specificationshall not be construed as a limitation to the present invention.

What is claimed is:
 1. A method for retrieving a transmission opportunity (TXOP) control in reverse direction grant, comprising: obtaining, by a reverse direction responder (RD responder), the TXOP control from a reverse direction initiator (RD initiator); enabling, by the RD responder, a multi-user multiple-input multiple-output (MU-MIMO) mode; sending, by the RD responder, a frame to a plurality of stations, which comprise the RD initiator; wherein the frame carries information that only requires the RD initiator to send back an acknowledgement.
 2. The method for retrieving a TXOP control in reverse direction grant according to claim 1, further comprising: when the RD initiator fails to correctly demodulate the frame, retrieving, by the RD initiator, the TXOP control by using a point coordination function inter-frame space (PIFS).
 3. A reverse direction responder (RD responder), comprising: an obtaining unit, configured to obtain a transmission opportunity (TXOP) control from a reverse direction initiator (RD initiator); a processing unit, configured to enable a multi-user multiple-input multiple-output (MU-MIMO) mode; a sending unit, configured to send a frame to a plurality of stations, which comprise the RD initiator; wherein the frame carries information that only requires the RD initiator to send back an acknowledgement. 